Update UF2 Family for nRF52833 boards

[jpconstantineau]

nRF52 bootloader project has updated the family for the nRF52833 to 0x621E937A for the nRF52833.

This will ensure that 840 firmware won't be able to be flashed to a 833 and vice-versa.

We need to update the Makefile here with some if statement to check for the nRf52833.

I don't know if there is anything else that needs updating.

[tannewt]

Here is a similar change done for ESP: #5771

[jpconstantineau]

Changes look relatively simple. Is there a variable that indicates the target? (For the nrf port)